At present, the touch panel generally has several types, such as a resistive type, a capacitive type, an optical type, an electromagnetic type, an ultrasonic wave type, and a LCD in-cell type that has three types of resistive, capacitive and optical. In a display device with an in-cell optical touch panel, a leakage current difference caused by different irradiation light intensities is used to determine that optical sensing elements in the in-cell optical touch panel whether are turned on or not and then serves as a basis for judging the in-cell optical touch panel whether is touched or not.
For example, the optical sensing element may include a thin film transistor (TFT). A TFT leakage current of the optical sensing element in cases that being touched by finger, being irradiated by ambient light and being touched (also being irradiated) by an light pen correspondingly may have a first current value, a second current value and a third current value. Thus, when the optical sensing element receives a large irradiated light intensity, the TFT leakage current Ids is consequently large, that is, the first current value is less than the second current value, and further less than the third current value. The charge difference generated by the difference of the TFT leakage currents is converted to be an output voltage through an integrator, and the output voltage value then is judged for determining whether the in-cell optical touch panel is touched or not.
Some of the present touch sensing manners still adopt(s) a differential sensing principle for judgment. Referring to FIG. 1, a source driver 12, touch sensors 16, gate drivers 14 and scanning sensors 18 are respectively disposed at the upside, the underside, the left side and the right side of the LCD. Generally, when a light stylus/pen 101 irradiates at an area of a liquid crystal panel 10, the touch sensors 16 would sense the change of voltage levels at the irradiated area with a high level and a low level, and the high level and the low level together form a group of judging signal as a basis for judging if the LCD device is touched or not by the light pen 10. However, when the light pen 10 irradiates at an edge of the liquid crystal panel 10, the touch sensors 16 only can sense the high level which would cause that the touch sensor 16 misjudges resulting from the incomplete judging signal.